Fasteners are known to the art in various forms.
In one known embodiment of such a device, a first element has the form of a flat wedge intended for insertion into a crack in a rock face, or some other form of opening in some other surface.
This known fastening device, having the planar wedge-shaped first element, is planar and tapers in the direction of its longitudinal axis and in relation to a central plane passing through the first element adjacent the second element. The wedge-shaped first element also decreases in width towards its free end.
Devices of the aforesaid nature may either have plane-parallel side surfaces or have a small wedge angle. Experience has shown that the wedge angle should be smaller than 5.degree..
The wedge portion of these known fasteners is also relatively long in relation to its cross-section, normally ratios in this regard being from 5 to 15.
Fasteners of the aforesaid kind are known to the art in which the first element has a longitudinal extension in a first plane which is rotated somewhat in relation to a second plane passing centrally through the second element.
Various types of wedge-shaped implements are known, for example, for splitting logs, in which a wedge part has a form of a single member and the wedge tip or point is turned 10.degree. in relation to a geometric central plane.
Such wedges have a large hammering or anvil surface at one end thereof and the wedge angle is quite large, for example larger than 10.degree. but smaller than 15.degree.. Such wedges are practically totally inelastic.
Consequently, driving wedges which are intended for splitting logs etc. are not suited for use in conjunction with fasteners for rock climbing or for mooring boats to rock surfaces.
With respect to prior art fasteners of the aforesaid kind, attachment of the device via the first element is effected exclusively through direct counter-directional clamping forces, in which a planar wedge surface is pressed against one wall of a crack, and the opposite planar wedge surface is pressed against the opposite wall of the crack. Any deformation which might occur is caused through the action of counter-directed forces acting on the same part or point on the wedge.
It has been found that in order to use such a wedge effectively the crack into which it is driven should have a width which more or less equals the maximum width of the wedge or which is slightly smaller than said width, and that the crack should be quite deep and preferably have a shape which conforms to the shape of the wedge.
Moreover, once driven into an ideal crack, the prior art fastener is extremely difficult to remove therefrom.
With reference to the state of the art beforedescribed it will be seen that one qualified technical problem resides in the provision of such fasteners that can be reliably secured in a crack whose width exceeds the maximum thickness of the wedge and/or whose configuration deviates from the configuration of the wedge.
Another technical problem resides in the provision of such a fastener with which the wedge-shaped element thereof can be subjected to torque such as to be brought into gripping co-action with mutually opposite walls of a crack, this torque causing diametriclly opposed wedge edges to grip against said crack walls.
Another technical problem resides in the provision of such a fastener so formed as to provide a reliable grip through the action of a large, substantially calculatable force, by observing material deformation caused by forces over and above the elastic deformation limit of the material and lying within the plastic deformation range.
With regard to the prior state of the art as described above, it is seen that a further qualified technical problem is one of providing a fastener of the kind intended for rock climbing, mooring boats to rock surfaces etc., with which the wedge-like first element of the device when inserted, for example, into a crack in a rock surface strives to engage the crack walls and to conform to the contours of the crack, such as to provide good contact between diametrically opposed and outwardly facing edge parts of the first element and the two engaging wall surfaces of the crack.
Still a further technical problem is one of providing such a fastener with which the diametrically opposed, outwardly facing edge parts of the first element co-acting with opposite walls of a crack can be brought into positive and reliable engagement therewith and readily released therefrom in a simple manner.
Another technical problem is one of providing means whereby the aforesaid co-action between the wedge-like first element of the fasteners and the walls of a crack can be effected with the aid of torque or torsional forces acting in the material of the wedge-like element, between two outwardly facing and mutually opposite edge parts thereof, so that the wedge will grip firmly in the crack through the agency of such internal forces as those occurring with plastic deformation.
Another technical problem is one of providing such a fastener which, with the aid of simple means, can be made to conform more readily to the contours of a crack determines the size of the contact surface formed between the two mutually opposed and outwardly facing edge parts, when the pressure forces taken-up shall function as torque on the wedge.